Short Message Service (SMS) is a communications protocol that allows the interchange of short text messages between mobile phone devices. SMS messages are typically sent via a Short Message Service Center (SMSC) of a mobile carrier, which uses a store-and-forward mechanism to deliver the messages. When a mobile phone is not reachable immediately for the delivery of the message, the SMSC stores the message for later retry.
SMS messages can be sent via gateways. Some gateways function as aggregators. An aggregator typically does not have the capacity to deliver the messages directly to the mobile phones. An aggregator typically interfaces with and relies upon the SMSC of a mobile carrier to deliver SMS messages.
Some gateways function as providers that are capable of sending text messages to mobile devices directly, without going through the SMSC of other mobile operators.
Text messaging between mobile phones can also be performed using other protocols, such as SkyMail and Short Mail in Japan.
Some mobile carriers provide email gateway services to allow text messages to be sent to mobile phones via email. For example, a non-subscriber of the mobile carrier may send a message to an email address associated with a mobile phone of a subscriber of the mobile carrier to have the message delivered to the mobile phone via text messaging.
Emails can also be sent to mobile phone devices via standard mail protocols, such as Simple Mail Transfer Protocol (SMTP) over Internet Protocol Suite (commonly TCP/IP, named from two of the protocols: the Transmission Control Protocol (TCP) and the Internet Protocol (IP)).
Short messages may be used to provide premium services to mobile phones, such as news alerts, ring tones, etc. The premium content providers may send the messages to the SMSC of the mobile operator using a TCP/IP protocol, such as Short Message Peer-to-peer Protocol (SMPP) or Hypertext Transfer Protocol, for delivery to a mobile phone; and the mobile phone is billed by the mobile operator for the cost of receiving the premium content.
Premium services may also be delivered via text messages initiated from the mobile phone. For example, a televoting service provider may obtain a short code to receive text messages from mobile phones; and when the user sends a text message to the short code, the mobile carrier routes the message to the televoting service provider and charges the user a fee, a portion of which is collected for the televoting service provider.